title: Caenorhabditis elegans centriolar protein SAS-6 forms a spiral that is consistent with imparting a ninefold symmetry.
abstract: Centrioles are evolutionary conserved organelles that give rise to cilia and flagella as well as centrosomes. Centrioles display a characteristic ninefold symmetry imposed by the spindle assembly abnormal protein 6 (SAS-6) family. SAS-6 from Chlamydomonas reinhardtii and Danio rerio was shown to form ninefold symmetric, ring-shaped oligomers in vitro that were similar to the cartwheels observed in vivo during early steps of centriole assembly in most species. Here, we report crystallographic and EM analyses showing that, instead, Caenorhabotis elegans SAS-6 self-assembles into a spiral arrangement. Remarkably, we find that this spiral arrangement is also consistent with ninefold symmetry, suggesting that two distinct SAS-6 oligomerization architectures can direct the same output symmetry. Sequence analysis suggests that SAS-6 spirals are restricted to specific nematodes. This oligomeric arrangement may provide a structural basis for the presence of a central tube instead of a cartwheel during centriole assembly in these species.
authors.affiliation: Laboratory of Biomolecular Research (LBR), Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
authors.forename: Manuel
authors.initials: M
authors.lastname: Hilbert
authors.forename: Michèle C
authors.initials: MC
authors.lastname: Erat
authors.forename: Virginie
authors.initials: V
authors.lastname: Hachet
authors.forename: Paul
authors.initials: P
authors.lastname: Guichard
authors.forename: Iris D
authors.initials: ID
authors.lastname: Blank
authors.forename: Isabelle
authors.initials: I
authors.lastname: Flückiger
authors.forename: Leanne
authors.initials: L
authors.lastname: Slater
authors.forename: Edward D
authors.initials: ED
authors.lastname: Lowe
authors.forename: Georgios N
authors.initials: GN
authors.lastname: Hatzopoulos
authors.forename: Michel O
authors.initials: MO
authors.lastname: Steinmetz
authors.forename: Pierre
authors.initials: P
authors.lastname: Gönczy
authors.forename: Ioannis
authors.initials: I
authors.lastname: Vakonakis
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D008854:Microscopy, Electron; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D029742:Caenorhabditis elegans Proteins; D018797:Cell Cycle Proteins; C497201:SAS-6 protein, C elegans
keywords: SAS-5; X-ray crystallography; centriolar architecture; electron microscopy; structure